a huge balloon, tied to a car’s vent-pipe, depicting the amount of exhaust emissions a car releases a day.

the "bursting earth" project is similar, but more dynamic. activists attach world globe balloons on exhaust pipes of cars in Berlin. the exhaust gas inflates the ballons. after the message becomes readable, there is a big "bang".

Thanks for bringing this to my attention. I've never seen such a visceral depiction of auto exhaust. Imagine a balloon 365 times its size for a year's worth of emissions, and we've got something really powerful. BTW, there is a San Francisco project called Park(ing) Day for some reason reminds me of this project.